In recent years, the research and development of magneto-optical recording media as high density and large capacity memories has been much carried out. In magneto-optical recording with magneto-optical recording media, a substrate that is made of glass, plastic, ceramic materials, etc. and is coated with a vertical magnetization film composed of metal-magnetic substance, is used as a recording medium, and information is recorded on the recording medium by switching the magnetization direction of a desired portion on the vertical magnetization film.
More concretely, when recording information, first, a recording medium is initialized by applying the external magnetic field from an external magnetic field generation device to the recording medium. With this operation, the magnetization direction of the vertical magnetization film on the recording medium is made uniform either upward or downward.
When the initialization is completed, a laser beam from light emitting means is irradiated on a desired recording portion of the recording medium. A temperature of the recording portion whereon the laser beam is irradiated rises, and when the temperature reaches or exceeds around the Curie point of the vertical magnetic film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. With this state, the magnetization direction is switched by applying an external magnetic field (bias magnetic field) whose magnetization direction is opposite to the set direction of the above-mentioned recording portion when initialized. The temperature of the recording portion decreases and eventually returns to the room temperature by stopping the irradiation of the laser beam on the recording portion. As described above, since the switched magnetization direction of the recording portion is kept, desired information can be recorded.
When reproducing information recorded in the above-mentioned way, a linearly polarized laser beam whose power is weaker than the one used during recording is irradiated on a recorded portion, and reflected light or transmitted light from the irradiated recording portion is detected. The recorded information is reproduced by detecting the rotation angle of the polarization plane of the reflected light or transmitted light. More precisely, since the rotation angle of polarization plane varies depending on the magnetization direction of the recorded portion (magnetic Kerr effect of magnetic Faraday effect), information can be read out optically with the use of the magnetic effect.
Therefore, magneto-optical recording as rewritable large capacity memory element has been focused recently. For rewriting information recorded on a recording medium, the following requirements must be fulfilled.
(1) Initializing the recording medium.
(2) Improving an external magnetic field (bias magnetic field) generation device or a recording medium whereon information can be rewritten without performing an erasing operation.
To meet requirement (1), however, an initialization device is separately demanded and two magneto-optical write heads may be needed, thereby causing the number of parts to increase. That is to say, in case of erasing information with a single magneto-optical write head, the same time taken for recording is required for erasing. In the mean time, in order to meet requirement (2), the composition and the thickness of the magnetic film need to be controlled.
For the above reasons, the most effective means the improvement of an external magnetic field (bias magnetic field) generation device satisfying requirement (2). Namely, information is recorded by, for example, maintaining the output of a laser beam at a fixed level and switching an external magnetic field at high speed. To switch the external magnetic field at high speed, a coil and a coil core for generating external magnetic field must be miniaturized to a great degree, and therefore, magnetic field generation areas become smaller. As a result, a magneto-optical write head and a recording medium must come close each other.
In order to get close the magneto-optical write head and the recording medium each other, a flying head in the shape of slider shown in FIG. 8 has been known and adopted. The flying head comprises a head slider means 31 and a head coil means 32. As shown in FIG. 8, the head coil means 32 is formed at an edge of the head slider means 31. The bottom surface of the head coil means 32 is aligned with the bottom surface of the head slider means 31. The head coil means 32 is connected to a power source 37 that generates a magnetic field, and the direction of the generated magnetic field varies depending on the polarity of the power source 37.
The head having the above configuration comes into contact with a recording medium at the time the recording medium starts rotating and stops rotating. Therefore, similar to computer hard disk cases where lubricating oil such as fluorocarbon oil is applied to the disk surface, lubricating oil 33 may be applied to a protective resin film 34 (see FIG. 8). With this application, the wear rate of the flying head and the magneto-optical recording medium can be reduced. Regarding the formation of the protective resin film 34, the protective resin film 34 is first applied to a vertical magnetization film 35 through the spin coating or other process and then hardened by an irradiation of ultraviolet light. The vertical magnetization film 35 is formed on a transparent substrate 36.
The magneto-optical medium, however, is portable, and this point differs from the above-mentioned hard disk. Therefore, in case liquid lubricating oil is applied to the surface of the magneto-optical recording medium, it is difficult to keep the oil staying on the surface, and therefore scratches may occur on the surface due to the absence of the liquid lubricating oil. This causes the reliability of the magneto-optical recording medium to remarkably lower.
Additionally, some manufacturers produce magneto-optical recording media without lubricating oil on their surface. In such a case, a problem arises, the magneto-optical recording media without lubricating oil are not compatible with magneto-optical recording media produced by other manufactures.
In the mean time, solid lubricating oil may be applied to a portion (the bottom surface of a head) of a flying head which comes into contact with the surface of a magneto-optical recording medium. In this way, however, solid lubricating oil to be applied to the flying head needs to have durability of some hundreds times as high as that of solid lubricating oil on the magneto-optical recording medium. Therefore, only applying lubricating oil to the flying head was not sufficient for solving the above problem.